1. Field of the Invention
This invention relates to an improved undervoltage circuit to operate, reset, and hold-in a circuit breaker.
2. Description of the Prior Art
Typically undervoltage trip releases (UVR's) have a movable solenoid or other device which can be energized by the normal voltage supply. When this supply voltage drops below a preset level a spring or other biasing mechanism moves the solenoid's armature to activate a mechanical circuit breaker. To automatically reset the solenoid once power is supplied again it has been common practice to supply a large current pulse from the available source voltage thereby requiring a relatively low impedance source. Where voltage matching transformers are required this low impedance requirement makes the transformers larger than they would otherwise be. Also, remote-control of the large current pulse by external means from areas demanding very high degrees of safety, like coal mines, is complicated.
The U.S. Pat. No. 3,657,603 to William M. Adams discloses an undervoltage disconnect circuit with automatic reset after the supply voltage reaches a predetermined normal operating level. However, it resets the circuit breaker by control means which require a low impedance control source. In our invention in resetting the undervoltage relay coil a repetitive pulse is applied to the UVR coil from a switched voltage doubler circuit. Neither the Adam's invention or any of the other known prior art allows the UVR to be reset and hold in the UVR with the low amount of power we employ.